Re: Realist --> Holmes

[P3D John Bercovitz <bercov@xxxxxxxxxxx>]

John Bercovitz wrote:

>Also, I think Holmes stereoscopes have lenses of about 7" focal 
>length.  (Alan?)  The cards have an image width of approximately 
>3".  So the ratio of focal length to image width is 7 divided by 
>3 or 2.3.  Contrast that with the 5-perf: It has an image width 
>of 21.4 or so and a focal length of about 35 for a ratio of focal 
>length to image width of 35/21.4 or 1.6.  So you can see that in 
>the 5-perf format, you are sitting much closer to the image; the 
>scene is very much wider.  

John R wrote:

>No it's not. 

Yes it is.  

"That's not argument; that's contradiction.  I paid for an argument. 
No you didn't.  Yes I did."  (You did watch Monty Python's Flying 
Circus, didn't you?)

>No it's not.  Having recently bought a Red Button Realist viewer 
>(thanks, Dr. T), I can say that when viewing in a Red Button and 
>in a Red Wing (Holmes stereoscope) viewer, the image size and the 
>image shape are nearly the same. 

What's the focal length on the Red Wing?  200 mm?  What's the image 
width?  80 mm?  80/200 = 0.4  = 23 degrees coverage

The focal length of the red button is 43 or 44 according to where 
you hear it from.  Image width of 5-perf is 21.4.  21.4/43 = .5  
= 28 degrees coverage

Hey, by golly, you're right.  The viewers are similar.  I was actually 
talking about the system (camera/viewer matchup) but maybe we really 
ought to be talking about the viewers instead.  It looks to me like 
viewing the Realist pair blown up in the Holmes is only 20% worse than 
viewing the original Realist pair in a red button.  The red button viewer 
is already 20% longer than the camera lens, unfortunatley, and so this 
worsens the error.  

Following the same method of calculation, if you have 6-" lenses on
your Red Wing, it will be no worse than the red button: 80/150 = .5

Going back to my original post (which I now rue) I would still crop the
print to make it fit the viewer even better rather than even worse.
And as I said in a subsequent post, it's only important if there are near,
familiar objects in the scene.

John B


------------------------------